Deep trench isolation structure of a high-voltage device and method for forming thereof

ABSTRACT

A deep trench isolation structure of a high-voltage device and a method of forming thereof. An epitaxial layer with a second type conductivity is formed on a semiconductor silicon substrate with a first type conductivity. A deep trench passes through the epitaxial layer. An ion diffusion region with the first type conductivity is formed in the epitaxial layer and surrounds the sidewall and bottom of the deep trench. An undoped polysilicon layer fills the deep trench.

BACKGROUND OF THE INVENTION

This nonprovisional application claims priority under 35 U.S.C. 119(a) on Patent Application No. 91125218 filed in TAIWAN on Oct. 25, 2002, which is herein incorporated by reference.

1. Field of the Invention

The invention relates to an isolation structure of a semiconductor device and a method of forming thereof, and more particularly to a deep trench isolation structure of a high-voltage device and a method of forming thereof.

2. Description of the Related Art

Recently, as the manufacturing techniques of semiconductor integrated circuits develop, the request of highly integrating controllers, memories, low-voltage operating circuits and high-voltage power devices on a single chip increases to achieve a single-chip system, in which the power device including vertical double-diffused transistor (VDMOS), lateral double-diffused transistor (LDMOS) and insulated gate bipolar transistor (IGBT), is used to increase power transform efficiency and decrease energy wastage. Since the high-voltage transistor and the low-voltage CMOS circuit device are provided on the single chip, an isolation structure is required to isolate the high-voltage device and the low-voltage device. Also, in order to fit in with a high breakdown voltage that is requested by the high-voltage device, the isolation structure must reach predetermined-depth isolation. Therefore, a deep trench isolation structure formed in a thick epitaxial layer has been developed by extra providing an epitaxial layer on a semiconductor substrate.

FIG. 1 is a cross-section of a conventional isolation structure of a high-voltage device. In a case of a P-type semiconductor silicon substrate 10, a N-type epitaxial layer 12 is provided on the P-type semiconductor silicon substrate 10, and a N-type buried layer (NBL) 14 is embedded between the N-type epitaxial layer 12 and the P-type semiconductor silicon substrate 10. Also, two P⁺-type deep trench isolation structures 16 are formed in the N-type epitaxial layer 12 to define a high-voltage area, and a plurality of field oxidation (FOX) regions 18 are formed on the upper surface of the N-type epitaxial layer 12 to isolate components within the high-voltage area. Moreover, a P-type body 22 is formed in the N-type epitaxial layer 12 between the second FOX region 18II and the third FOX region 18III, and a pair of N⁺-type diffusion regions 24 and a pair of P⁺-type diffusion regions 26 that are respectively electrically connected to exterior wires are formed in the P-type body 22. Furthermore, a gate structure 28 is formed on the surface of the P-type body 22.

A N⁺-type sinker 20 is formed in the N-type epitaxial layer 12 between the first FOX region 18I and the second FOX region 18II, and electrically connected to exterior wires formed overlying the N-type epitaxial layer 12.

In manufacturing the P⁺-type deep trench isolation structure 16, a deep trench formed in the N-type epitaxial layer 12 is filled with an oxide layer, and then ion implantation is employed to implant B⁺ ions into the oxide layer by, and finally thermal annealing is employed to diffuse the B⁺ ions in the oxide layer. For spreading the B⁺ ions around within the deep trench, however, the procedure time of the thermal annealing is very long, resulting in increased thermal budget. Also, since the thermal annealing makes the B⁺ ions diffuse both toward a vertical direction and a lateral direction, the width W of the P⁺-type deep trench isolation structure 16 increases as the depth H of the P⁺-type deep trench isolation structure 16 increases. When the deep trench 16 is requested to reach predetermined-depth isolation, the lateral size of the P⁺-type deep trench isolation structure is also increases, resulting in the required size of a chip being increased.

Accordingly, how to forming a deep trench isolation structure with decreasing thermal budget and reducing the lateral size of the deep trench isolation structure to solve the problems caused by the prior method is called for.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide a deep trench isolation structure of a high-voltage device and a method of forming thereof, in which a P⁺-type diffusion region and an undoped polysilicon layer within a deep trench are formed as a P⁺-type deep trench isolation structure.

To achieve these and other advantages, the invention provides a deep trench isolation structure of a high-voltage device. An epitaxial layer with a second type conductivity is formed on a semiconductor silicon substrate with a first type conductivity. A deep trench passes through the epitaxial layer. An ion diffusion region with the first type conductivity is formed in the epitaxial layer and surrounds the sidewall and bottom of the deep trench. An undoped polysilicon layer fills the deep trench.

To achieve these and other advantages, the invention provides a method of forming a deep trench isolation structure of a high-voltage device. First, a semiconductor silicon substrate with a first type conductivity is provided with an epitaxial layer with a second type conductivity. Then, an oxide layer is formed on the epitaxial layer. Next, photolithography and etching are used to form a deep trench which passes through the oxide layer and the epitaxial layer. Next, an oxide liner is formed on the sidewall and bottom of the deep trench. Next, ion implantation is used to form an ion diffusion region with the first type conductivity which is formed in the epitaxial layer and surrounds the sidewall and bottom of the deep trench. Next, an undoped polysilicon layer is formed on the entire surface of the semiconductor silicon substrate to fill the deep trench. Finally, the oxide layer and the undoped polysilicon layer outside the deep trench are removed until the surface of the undoped polysilicon layer is leveled with the surface of the epitaxial layer.

Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 is a cross-section of a conventional isolation structure of a high-voltage device; and

FIGS. 2A to 2G are cross-sections of a method of forming a deep trench isolation structure of a high-voltage device according the present invention.

FIG. 3 is a cross-section of a high-voltage device with P⁺-type deep trench isolation structures according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the present invention is now described with reference to FIGS. 2A through 2G, in which a P-type semiconductor substrate is provided to form a P⁺-type deep trench isolation structure within a high-voltage device area. In another case, the present invention can apply to the formation of an N⁺-type deep trench isolation structure.

FIGS. 2A to 2G are cross-sections of a method of forming a deep trench isolation structure of a high-voltage device according the present invention. In FIG. 2A, an N-type epitaxial layer 32 is formed on a P-type semiconductor silicon substrate 30, and an oxide layer 34 is formed on the N-type epitaxial layer 32. Preferably, the thickness of the N-type epitaxial layer 32 is approximately equal to the predetermined depth H of the deep trench isolation structure. In addition, for product demands, an N-type buried layer (NBL) may be formed between the N-type epitaxial layer 32 and the P-type semiconductor silicon substrate 30. Then, in FIG. 2B, a photoresist layer 36 having a deep trench pattern is formed on the oxide layer 34 to define the width W of the deep trench isolation structure. Next, using the photoresist layer 36 as a mask, the exposed area of the oxide layer 34 is etched to form an opening 38.

Next, in FIG. 2C, using the oxide layer 34 as a mask, the exposed area of the N-type epitaxial layer 32 under the opening 38 is etched until the surface of the P-type semiconductor silicon substrate 30 is exposed, thus a deep trench 40 is formed. Next, in FIG. 2D, using an ion implantation 42 with P⁺-type dopants, such as a tilt-angle ion implantation with B⁺ ions, a P⁺-type diffusion region 44 is formed in the sidewall and bottom of the deep trench 40. Then, an oxide liner 46 is formed on the sidewall and bottom of the deep trench 40 to repair the damaged surface caused by the ion implantation 42.

Thereafter, in FIG. 2E, an undoped polysilicon layer 48 is deposited on the entire surface of the P-type semiconductor silicon substrate 30 to fill the deep trench 40. Then, the thermal annealing is used to reduce the grain size of the undoped polysilicon layer 48 to prevent the deep trench 40 being partially filled with the undoped polysilicon layer 48 from voids formed in the undoped polysilicon layer 48. Next, in FIG. 2F, using an etching back process, the undoped polysilicon layer 48 outside the deep trench 40 is removed until the surface of the oxide layer 34 is exposed. Finally, in FIG. 2G, using chemical mechanical polishing (CMP), the oxide layer 34 and a part of the undoped polysilicon layer 48 are removed until the surface of the N-type epitaxial layer 32 is exposed. Then, the thermal annealing is used to re-grow grains of the undoped polysilicon layer 48. This completes P⁺-type deep trench isolation structure.

The present invention provides the P⁺-type diffusion region 44 and the undoped polysilicon layer 48 within the deep trench 40 as the P⁺-type deep trench isolation structure. Since the P⁺-type diffusion region 44 is formed on the sidewall and bottom of the deep trench 40 by the ion implantation 42, it is unnecessary to use the thermal annealing to drive the vertical diffusion mechanism of the P⁺-type dopants, resulting in decreased thermal budget. Also, compared with the conventional deep trench isolation structure having an H/W ratio equal to 1.2 by using thermal annealing, the present invention can control the H/W ratio of the P⁺-type deep trench isolation structure at 4˜3. This can reduce the surface size of the P⁺-type deep trench isolation structure.

The above-described P⁺-type deep trench isolation structure, including the P⁺-type diffusion region 44 and the undoped polysilicon layer 48 within the deep trench 40 can be integrated into a high-voltage device. Preferably, the high-voltage device has a drain terminal with a supply voltage exceeding 5V. FIG. 3 is a cross-section of a high-voltage device with P⁺-type deep trench isolation structures according to the present invention. Elements in FIG. 3 are substantially similar to those in FIGS. 2A˜2G, with the similar portions omitted herein. In the P-type semiconductor silicon substrate 30, an N-type buried layer (NBL) 33 is embedded between the N-type epitaxial layer 32 and the P-type semiconductor silicon substrate 30. Also, two P⁺-type deep trench isolation structures, including the P⁺-type diffusion region 44 and the undoped polysilicon layer 48, are formed in the N-type epitaxial layer 32 to define a high-voltage area, and field oxidation (FOX) regions 60I, 60II and 60II are formed on the upper surface of the N-type epitaxial layer 32 to isolate components within the high-voltage area. A N⁺-type sinker 50 is formed in the N-type epitaxial layer 32 between the first FOX region 60I and the second FOX region 60II, and electrically connected to exterior wires formed overlying the N-type epitaxial layer 32. Moreover, a P-type body 52 is formed in the N-type epitaxial layer 32 between the second FOX region 60II and the third FOX region 60III, and a pair of N⁺-type diffusion regions 54 and a pair of P⁺-type diffusion regions 56 that are respectively electrically connected to exterior wires are formed overlying the P-type body 52. Furthermore, a gate structure 58 is formed overlying the P-type body 52.

While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements. 

1. A semiconductor device, comprising: a semiconductor silicon substrate with a first type conductivity; an epitaxial layer with a second type conductivity different from the first type conductivity which is formed on the semiconductor silicon substrate, wherein the epitaxial layer comprises at least a deep trench and the epitaxial layer surrounding both sidewalls of the deep trench has the same type conductivity; an ion diffusion region with the first type conductivity which is formed in the epitaxial layer and surrounds the sidewall and bottom of the deep trench; and an undoped polysilicon layer filling the deep trench; wherein, the combination of the ion diffusion region and the undoped polysilicon layer serves as a deep trench isolation structure; wherein the semiconductor device comprises two deep trench isolation structures to define a high-voltage area; wherein the high-voltage area comprises: a buried layer with the second type conductivity formed between the epitaxial layer and the semiconductor silicon substrate; a plurality of field oxidation regions formed in the epitaxial layer, wherein a first field oxidation region, a second field oxidation region and a third field oxidation region are successively arranged between the two deep trench isolation structures; a sinker with the second type conductivity formed in the epitaxial layer between the first field oxidation region and the second field oxidation region; a body with the first type conductivity formed in the epitaxial layer between the second field oxidation region and the third field oxidation region; a gate structure formed overlying the body; a pair of first diffusion regions with the second type conductivity formed in the body and laterally adjacent to the gate structure; and a pair of second diffusion regions with the first type conductivity formed in the body and laterally adjacent to the first diffusion regions, respectively.
 2. The semiconductor device as claimed in claim 1, wherein the first type conductivity is P-type, and the second type conductivity is N-type.
 3. The semiconductor device as claimed in claim 2, wherein the ion diffusion region is a P⁺-type ion diffusion region.
 4. The semiconductor device as claimed in claim 1, wherein the first type conductivity is N-type, and the second type conductivity is P-type.
 5. The semiconductor device as claimed in claim 2, wherein the ion diffusion region is a N+-type ion diffusion region.
 6. The semiconductor device as claimed in claim 1, further comprising an oxide liner formed on the sidewall and bottom of the deep trench.
 7. The semiconductor device as claimed in claim 1, wherein: the buried layer is a N⁺-type ion diffusion region; the sinker is a N⁺-type ion diffusion region; the body is a P-type body; the first diffusion region is a N⁺-type ion diffusion region; and the second diffusion region is a P+-type ion diffusion region.
 8. A high-voltage device, comprising: a semiconductor silicon substrate with a first type conductivity; an epitaxial layer with a second type conductivity different from the first type conductivity which is formed on the semiconductor silicon substrate, wherein the epitaxial layer comprises at least two deep trenches; at least two deep trench isolation structures formed in the epitaxial layer to define a high-voltage area and the epitaxial layer surrounding both sidewalls of the deep trenches has the same type conductivity; and a high-voltage transistor formed within the high-voltage area; wherein, each deep trench isolation structure comprises: an ion diffusion region with the first type conductivity formed in the epitaxial layer and surrounding the sidewall and bottom of the deep trench; and an undoped polysilicon layer filling the deep trench; wherein the high-voltage area comprises: a first field oxidation region, a second field oxidation region and a third field oxidation region, which are formed in the epitaxial layer and successively arranged between the two deep trench isolation structures; a buried layer with the second type conductivity, which is formed between the epitaxial layer and the semiconductor silicon substrate; a sinker with the second type conductivity, which is formed in the epitaxial layer between the first field oxidation region and the second field oxidation region and connected to the buried layer; a body with the first type conductivity, which is formed in the epitaxial layer between the second field oxidation region and the third field oxidation region and formed overlying the buried layer; a gate structure formed overlying the body; a pair of first diffusion regions with the second type conductivity formed in the body and laterally adjacent to the gate structure; and a pair of second diffusion regions with the first type conductivity formed in the body and laterally adjacent to the first diffusion regions, respectively.
 9. The high-voltage device as claimed in claim 8 wherein the first type conductivity is P-type, and the second type conductivity is N-type.
 10. The high-voltage device as claimed in claim 8 wherein the ion diffusion region is a P⁺-type ion diffusion region.
 11. The high-voltage device as claimed in claim 8 wherein: the buried layer is a N⁺-type ion diffusion region; the sinker is a N⁺-type ion diffusion region; the body is a P-type body; the first diffusion region is a N⁺-type ion diffusion region; and the second diffusion region is a P⁺-type ion diffusion region.
 12. The high-voltage device as claimed in claim 8 wherein the first type conductivity is N-type, and the second type conductivity is P-type.
 13. The high-voltage device as claimed in claim 8 further comprising an oxide liner formed on the sidewall and bottom of the deep trench. 